Pontiac 2003 Sunfire Owner's Manual page 236

Park the vehicle on a level surface. You can
remove the coolant surge tank pressure cap
when the cooling system, including the coolant
surge tank pressure cap and upper radiator hose, is
no longer hot. Turn the pressure cap slowly
counterclockwise (left) about two or two and
one-half turns. If you hear a hiss, wait for that to
stop. This will allow any pressure still left to
be vented out the discharge hose.
3. Then fill the coolant surge tank with the proper
mixture, to the hash mark on the label. Wait
about five minutes, then check to see if the level is
below the hash mark. If the level is below the
hash mark, add additional coolant to bring the level
up to the hash mark. Repeat this procedure until
the level remains constant at the hash mark
for at least five minutes.
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